Television synchronizing and control system



May 6,1941. M. CAWEIN TELEVISION SYNCHRONIZING AND CONTROL SYSTEM FiledOct. 5, 1938 mohkmmzuo Kin-50mm. uz 3 INVENTOR MADISON CAWEIN M mohouhmnATTORNEY Patented May 6, 1941 TELEVISION SYNCHRONIZING AND @ONTROLSYSTEM Madison Cawein, Manhasset, N. Y., ass! or to HazeltineCorporation, a. corporation oi Delaware Application October 5, 1938Serial No. 233,372

13 Claims.

This invention relates to television receiving apparatus and moreparticularly to synchronizing and control systems for such apparatus.The invention is especially directed to the provision of a combinedsychronizing-signal-separating and automatic amplification controlsystem for television receivers.

In accordance with present television practice, a transmitted signalcomprises a carrier wave modulated by light-modulation componentsrepresentative of varying light values in successive incremental areasof an image being transmitted and of its average backgroundillumination, and synchronizing-modulation components which correspondto initiations of successive lines and fields in the scanning of theimage. In signals generally referred to as negatively modulated signals,decreases in carrier amplitude correspond to increases in light values.The synchronizing components extend in the black direction; that is,they are represented by increases in carrier amplitude and they haveamplitude values which extend outside of the amplitude range of thelight-modulation components.

At the receiver, a beam is so deflected as to .scan and illuminate atarget in a series of fields of parallel lines. Thesynchronizing-modulation components of the received signal are utilizedto control the scanning apparatus so as to synchronize its operationwith that of similar apparatus utilized at the transmitter in developingthe signal. The intensity of the cathode ray is controlled by thevideo-frequency components of the signal, as well as by theunidirectional background illumination voltage developed in thereceiver, thereby to reconstruct the transmitted image.

Essential functions which must be performed in a television receivingsystem of the type described include deriving from the signal-carrierwave the line-frequency and field-frequencysynchronizing components orpulses separate from the other or light-modulation components. Also,certain operating characteristics of the receiver, for example, theamplification or gain, must be controlled automatically in accordancewith the intensity of thereceived carrier wave and independent ofitslight-modulation components, that is, as determined by the power ofits transmitting station, its distance, fading, etc. For this purposethere is usually developed a control effect, for example, aunidirectional bias voltage, which is proportional to the averagecarrier intensity and independent of light-mod ulation components, whichcontrol effect is utilized to produce the desired control of theoperating characteristics of the receiver. Various methods haveheretofore. been devised for performing these functions but, in generalthey 231E einvolved trelatively complicated and/or unappara us, 0entirely satisfactorylr otherwise have not been It is an object of thepresent inventi provide, in a. television signal-reproducing tem whereinthe received carrier wave is modulated by light-modulation componentsand synchronizing-modulation components having amplitude values outsidethe amplitude range of the light components, improved means for derivingfrom the received signal-carrier wave the synchronizing componentsseparate from the other modulation components.

It is a further object of the invention to provide, in a system of thecharacter described combined means for developing both a unidi rectionalcontrol-bias voltage representative of the average intensity of thereceived signal and independent of the light-modulation components andthe separated synchronizing-modulation components themselves.

In accordance with the present invention, there is provided a televisionreceiver adapted to reproduce a signal-carrier wave the amplitude ofwhich may vary at the receiver and having lightmodulation components andsynchronizing-modulation components having amplitude values outside theamplitude range of the light-modulation components. The receiverincludes means including a modulated-carrier signal detector forderiving the modulation components from the signal-carrier wave, meansfor controlling the detector in accordance with the amplitude of thesignal input to the detector to limit detection thereby to saidmodulation components outside the amplitude range of thelight-modulation components regardless of variations of thesignalll'lllllt amplitude to the detector and means for utilizing thesedetected components for controllmg the operation of the receiver, forexample synchronizing the receiver. In accordance with one embodiment ofthe invention, a rectifier is provided for developing from the carrierwave a control effect, such as a unidirectional bias voltage,proportional to the intensity of the received signal and independent oflight-modulation components. There is also provided a detector forderiving modulation components from the carrier wave and a portion ofthe control eflect or unidirectional bias voltage is utilized to controlthe detector to eflect detection only of the desired portion oi theamplitude range of the received carrier wave. The total control eflector bias voltage is preferably utilized to control an operatingcharacteristic of the receiver. for example, to effect automaticamplification control.

For a better understanding of the invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

In the accompanying drawing, Fig. l is a circuit diagram, partiallyschematic, of a television receiver or reproducing system includingcircuits embodying the present invention, while Fig. 2 is a graphrepresenting certain operating charw acteristics oi the system of Fig. 1to aid in the understanding of the invention.

Referring now more particularly to the drawing, the system thereillustrated comprises a receiver oi the superheterodyne type includingan antenna system IO-II connected to a radio-frequency amplifier I2 towhich is connected, in casor cade in the order named, anoscillator-modulator 13, an intermediate-frequency amplifier I4, adetector I5, a video-frequency amplifier I6 and an image-reproducingdevice II which may, for example, be a cathode-ray signal-reproducingtube,

these stages or units constituting the main signaltranslating channel ofthe receiver. A line-frequency generator I3 and a field-frequencygenerator ii! are also coupled to the output circuit of the amplifierI4, by way of synchronizing-signal-separating apparatus presently to bedescribed, and to the scanning elements of the image-reproducing deviceIT, in the conventional manner. The stages or units Ill-I9 may all be ofconventional well-known construction, so that detailed illustrations anddescriptions thereof are deemed unnecessary herein.

Referring briefly, however, to the operation of the system describedabove, television signals intercepted by the antenna circuit Ill-Ill areselected and amplified in the radio-frequency amplifier I2 and suppliedto the oscillator-modulator I3, where they are converted tointermediate-frequency signals which, in turn, are selectively amplifiedin the intermediate-frequency amplifier I 4 and delivered to thedetector I5. The modulation components of the signal are derived by thedetector I5 and are supplied to the video-frequency amplifier I6 whereinthey are amplified and from which they are supplied ,in the usual mannerto a brilliancy-control element of the image-reproducing device II.

The intensity of the scanning beam oil the device I1 is thus modulatedor controlled in accordance with the light-modulation voltages impressedupon the control element of the device in the usual manner. Saw-toothcurrent waves generated in the line-frequency and field-frequencygenerators I8 and I9, respectively, which are controlled bysynchronizing-voltage pulses supplied from the apparatus of thisinvention, as presently to be explained, are applied to the scanningelements of the device I I to produce electric scanning fields, therebyto deflect the scanning ray in directions normal to each other so as totrace a rectilinear scanning pattern on the screen of the tube andthereby to reconstruct the transmitted image.

Referring now more particularly to the portion of the system of Fig. 1embodying the present invention, for the purpose of deriving from thereceived carrier wave the synchronizing components separate from theother modulation components, as well as a unidirectional control-biasvoltage, there is provided a control signal-translating channelcomprising a vacuum-tube amplifier 20, a rectifier 2|, and a detector22. The tube 20 may be of any suitable type having an input circuit,comprising a coupling condenser 23 and leak resistor 24, connected tothe output circuit or the amplifier I4. A suitable biasing battery 20ais included in the cathode circuit of this tube. The output circuit orthe tube 20 includes the primary winding 25 of an intermediate-frequencytransformer, the secondary winding 26 of which is coupled to rectifier2i and detector 22, as shown. The windings 25 and 26 are each tuned tothe intermediate frequency by condensers 26a and 25a, respectively, andsuitable shunt resistors 25b and 26b are connected across these tunedcircuits, as shown.

The rectifier 2| is provided for developing the control-bias voltage andincludes a load circuit comprising a parallel-connected voltage dividerresistor 21 and condenser 28 having a large time constant. This timeconstant should be considerably greater than the period of theline-synchronizing pulses. utilizing, for example, 30 frames (60 fields)or 441 lines per second, the resistor 21 may be of the order of 0.5megohm and the condenser 28 of the order of 500 micro-microfarads,providing a time constant of 250 microseconds. The negative terminal ofthe resistor 21 is connected, by way of a suitable filter includingseries resistor 3| and shunt condenser 32 and suitable conductorsindicated as A. V. C., to the control electrodes of one or more vacuumtubes included in the amplifier I2, oscillator-modulator I3, andamplifier I4, as shown.

The detector 22 is provided for the purpose of deriving thesynchronizing pulses separate from the other modulation components, andto this end is designed to detect the modulation envelope of thereceived carrier wave and includes a load circuit comprising aparallel-connected resistor 29 and condenser 30. The time constant ofthis circuit is considerably less than that of the load circuit 21, 28and short compared to the duration of the line-synchronizing pulses sothat the modulation voltages are developed thereacross. The load circuitof detector 22 is completed through a resistor 33 and a portion ofvoltage divider 21 determined by an adjustable tap 35, both by-passed bya condenser 34, resistor 33 and condenser 34 also serving as a filterfor the bias voltage derived from rectifier 2 I. Thus, a predeterminedportion oi. the unidirectional bias voltage developed by the rectifieris applied as a negative delay bias to the anode of detector 22, so thatthe latter is effective to detect only a portion of the amplitude rangeof the carrier, more particularly, only the synchronizing-modulationcomponents. The input circuits of the line-frequency and field-frequencygenerators I8 and I9 are connected across the load circuit of thedetector 22 by way of suitable leads 36 and condenser 34. Conventionalcircuits may be included in the generators I8 and I9 for separating theline-synchronizing and field-synchronizing pulses from each other.

The operation of the system in accordance with the present invention maybest be explained with reference to the graph of Fig. 2, in which curveA illustrates the characteristic of the detector 22, the abscissaerepresenting applied. alternat- For conventional systems ing voltage andthe ordinates representing the load current or the detector 22. Theapplied voltage is illustrated by curve C which shows the envelope ofthe negatively modulated-carrier wave the amplitude of which may vary atthe receiver, as developed in the output circuit of theintermediate-frequency amplifier I4 and applied by way of the tube 20and transformer 25, 28 to the diodes 2| and 22. For the purpose ofsimplicity, only a few line-frequency cycles are shown. Thelight-modulation components and synchronizing-modulation components areindicated at L and S, respectively, the latter, it will be noted,extending beyond the amplitude range oi the former. Signal levelscorresponding to white and black are indicated at W and B, respectively,in the figure.

The diode 2i operates as a conventional peak rectifier, passing currentonly during the occurrence of synchronizing pulses, which represent thepeak values of the modulated-carrier wave, this being determined by thelarge time constant circuit provided by the resistor 21 and condenser28. There is thus built up across the load circuit 21, 28 aunidirectional voltage of a value such as indicated by the arrow labeledA. V. C. in Fig. 2, which is the peak rectified applied signal. That is,the average value of this voltage is proportional to the maximumamplitude of the carrier wave and independent of lightmodulationcomponents. The filter comprising the resistor 3| and condenser 32serves to remove residual fluctuations from the rectified voltage andthe resultant steady unidirectional bias voltage is impressed negativelyon the control grids of one or more of the tubes in the stages l2, l3and H to control the amplification of these stages inversely inaccordance with the maximum values of the carrier-wave amplitude andindependent of light-modulation components. Thus, the output signalintensity of the main signal-translating. channel is maintained within arelatively narrow range for a wide range of received signal intensitiesdue to the effect of the control-bias voltage developed by rectifier 2|,the bias voltage being variable in accordance with the intensity of thereceived carrier wave and independent of its light-modulationcomponents.

The detector 22 constitutes a modulated-carrier signal-detecting meansand operates similarly to the rectifier 2 I, as just described, exceptthat the time constant of its load circuit is such that the modulationenvelope of the signal is detected. Further, in this case, a part of theunidirectional voltage developed by the rectifier 2| is applied to theanode of diode 22 as a negative bias to limit detection thereby, theapplied bias being variable in accordance with the amplitude of thesignal input to the detector. Referring again to Fig. 2, it will be seenthat the synchronizing components S represent a certain percentage ofthe modulation amplitude range of the carrier wave, for example, 25 percent. The tap 35, therefore, is adjusted so that a delay bias voltagecorresponding to at least a portion and preferably approximately 75 percent of the total voltage developed by the rectifier 2! is appliednegatively to the anode of the detector 22, this negative bias, asindicated in Fig. 2, serving to delay the detector 22 so that it isoperative to detect, that is to pass current representative of, only theportion of the amplitude range of the carrier constituting thesynchronizing-modulation components or pulses and its output is thuslimited to modulation components outside the amplitude range of thelightmodulation components of the received signal regardless ofvariations of the signal-input amplitude to the detector. There is thusdeveloped across the load circuit of the detector 22 thesynchronizing-modulation components or pulses free from thelight-modulation components of the carrier, as illustrated by curve e ofFig. 2. These pulses are applied to the generators l8 and I9, in whichconventional separating apparatus serves to separatetheline-synchronizing and fieldsynchronizing pulses and these pulses areutilized to maintain the generators l8 and I9, respectively, insynchronism with the corresponding apparatus at the transmitter, in theusual manner. It is, therefore, seen that the arrangement of Fig. 1comprises a television receiver adapted to reproduce a signal-carrierwave, the amplitude of which may vary at the receiver, and which haslight-modulation components and synchronizingsignal components havingamplitude values outside the amplitude range of the light-modulationcomponents. The arrangement comprises means including amodulated-carrier signal detector 22 for deriving modulation componentsof the received carrier wave, as well as means for developing a biasacross resistor 21 for controlling the detector 22 in accordance withthe amplitude of the signal input to the detector to limit detectionthereby to the modulation components outside the amplitude range of thelight-modulation components regardless of variations of the signalinputamplitude to the detector. Furthermore, means are provided including theconductor 36 for utilizing the detected components for controlling anoperation of the receiver, specifically for controlling thesynchronization of the receiver.

The system of the present invention thus serves to derive from thesignal carrier both the unidirectional bias voltage proportional to theintensity of the modulated-signal carrier and independent of itslight-modulation components and the synchronizing-modulation componentsseparate from the other modulation components.

While there has been described what is at present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims tocover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A television receiver adapted to reproduce a signal-carrier wave theamplitude of which may vary at the receiver and having light-modulationcomponents and synchronizing-modulation components having amplitudevalues outside the amplitude range of said light-modulation componentscomprising, means including a modulated-carrier signal detector forderiving modulation components from a received signal-carrier wave,means for controlling said detector in accordance with the amplitude ofthe signal input to said detector to limit detection thereby to saidmodulation components outside said amplitude range of saidlight-modulation components regardless of variations of the signal-inputamplitude to said detector, and means for utilizing said detectedcomponents for controlling the operation of said receiver.

2. A television receiver adapted to reproduce a signal-carrier wave theamplitude of which may vary at the receiver and having light-modulationcomponents and synchronizing modulation components having amplitudevalues outside the amplitude range of said light-modulation componentscomprising, a means for deriving from said signal a control-bias voltagevariable in accordance with the intensity oi the carrier wave andindependent of its light-modulation components, a vacuum-tube repeaterfor translating the signal, means for applying said bias voltage to saidrepeater to limit the translation 01. the signal thereby to the portionof the signal including said modulation components outside said range ofsaid light-modulation components, and means for utilizing the signalcomponents translated by said repeater for synchronizing the operationof said receiver.

3. A television receiver adapted toreproduce a signal-carrier wave theamplitude of which may vary at the receiver and having light-modulationcomponents and synchronizing-modulation components having amplitudevalues outside the amplitude range of said light-modulation componentscomprising, means including a modulated-carrier signal detector forderiving modulation components from a received signal-carrier wave,means for biasing said detector in accordance with the amplitude of thesignal input to said detector to limit detection thereby to saidmodulation components outside said amplitude range of saidlight-modulation components regardless of variations of the signal-inputamplitude to said detector, and means for utilizing said detectedcomponents for synchronizing the operation of said receiver. R

4. A television receiver adapted to reproduce a signal-carrier wave theamplitude oi? which may vary at the receiver and having a portion of itsamplitude range modulated by light-modulation components and anotherportion of its amplitude range modulated by synchronizing-modulationcomponents comprising, means including a modulatedcarrier signaldetector for deriving modulation components from a receivedsignal-carrier wave, means for controlling said detector in accordancewith the amplitude of the signal input to said detector to limitdetection thereby to said portion of said amplitude range of saidcarrier wave modulated by said synchronizingmodulation componentsregardless of variations of the signal-input amplitude to said detector,

and means for utilizing said detected components for synchronizing theoperation of said receiver.

5. A television receiver adapted to reproduce a signal-carrier wave theamplitude of which may vary at the receiver and having light-modulationcomponents and synchronizing-modulation components having amplitudevalues outside the amplitude range of said light-modulation componentscomprising, means including a modulated-carrier signal detectorforderiving modulation components from a received signal-carrier wave,means for deriving a control eil'ect proportional to the intensity ofsaid carrier wave and independent of its light-modulation components,means for utilizing said control efiect for controlling said detector tolimit detection thereby to said modulation components outside said rangeof said light-modulation components,

' and means for utilizingsaid detected components bias voltageproportional to the intensity of said carrier wave and independent ofits light-modulation components, means for applying at least a portionof said bias voltage negatively to said detector to limit detectionthereby to said modulation components outside said range of saidlight-modulation components, and means for utilizing said detectedcomponents for synchronizing the operation of said receiver.

7. A television receiver adapted to reproduce a signal-carrier wavehaving light-modulation components and synchronizing-modulationcomponents having amplitude values outside the amplitude range of saidlight-modulation components comprising, means for deriving from areceived signal-carrier wave a control eflect proportional to theintensity of the carrier wave and independent of its light-modulationcomponents, means for detecting said carrier wave to derive itsmodulation'components, means for utilizing said control eil'ect forcontrolling said detecting means to limit detection thereby to saidmodulation components outside said range of said light-modulationcomponents, means for utilizing said control eiiect for controlling anoperating characteristic of the receiver, and means for utilizing saiddetected components for synchronizing the operation of said receiver.

8. A television receiver adapted to reproduce a signal-carrier wavehaving light-modulation components and synchronizing-modulationcomponents having amplitude values outside the amplitude range of saidlight-modulation components, said carrier wave having a wide rangeofsignal-input intensities comprising, a modulated-carriersignal-detecting and -reproducing means, means for deriving from areceived signalcarrier wave a control-bias voltage proportional to theintensity of said carrier wave and independent of its light-modulationcomponents, means for detecting said carrier wave to derive itsmodulation components, means for applying at least a portion of saidbias voltage negatively said modulation components outside said range ofsaid light-modulation components, means for utilizing said control-biasvoltage for maintaining the average amplitude, independent of lightmodulation, of the carrier input to said signaldetecting and-reproducing means within a relatively narrow range for a wide range ofreceived signal-input intensities, and means for utilizing said limiteddetected components for synchronizing the operation of said receiver.

9. A television receiver adapted to reproduce a signal-carrier wavehaving light-modulation components and line-synchronizing andfieldsynchronizing-modulation components having amplitude values outsidethe amplitude range of said light-modulation components, said carrierhaving a wide range of signal-input intensities comprising, amodulated-carrier signal-detecting and -reproducing means, a rectifierhaving a load circuit with a time constant long compared to the periodof said line-frequency synchronizing components for deriving from saidsignal a control-bias voltage variable in accordance with the intensityof the carrier wave independent of its light-modulation components,means including a modulated-carrier signal detector having a loadcircuit with a time constant short compared with the duration of saidline-frequency pulses for deriving from said carrier wave its modulationcomponents, means for applying at least a portion of said bias voltagenegatively to said detector to limit detection thereby to saidmodulation components outside said range of said light-modulationcomponents, means for utilizing said controlebias voltage formaintaining the average amplitude, independent of light modulation, ofthe carrier input to said signaldetecting and -reproducing means withina relatively narrow range for a wide range of received signal-inputintensities, and means for utilizing said limited-detected componentsfor synchronizring the operation of said receiver.

10. A television receiver adapted to reproduce a signal carrier wavehaving light-modulation components and synchronizing-modulationcomponents having amplitude values outside the -amplitude range oi saidlight-modulation components comprising, a rectifier having a loadcircuit including a voltage divider resistor for deriving from saidsignal a control-bias voltage proportional to the intensity of thereceived carrier wave and independent of its light-modulationcomponents, means including a modulatedcarrier signal detector forderiving modulation components trom saidcarrier wave, a connectionbetween said voltage divider and said detector for applying at least aportion of said bias voltage negatively to said detector to limitdetection thereby to said modulation components outside said range ofsaid light-modulation components, and means for utilizing said detectedcomponents for synchronizing the operation of said receiver.

11. A. television receiver adapted to reproduce a signal-carrier wavehaving light-modulation components and synchronizing-modulationcomponents having amplitude values outside the amplitude range of saidlight-modulation components comprising, a rectifier having a loadcircuit including a voltage divider resistor for deriving from saidsignal a control-bias voltage proportional to the intensity of thereceived carrier wave and independent of its light-modulationcomponents, means including a modulated-carrier signal detector forderiving modulation components from said carrier wave, a

connection between said voltage divider and said detector for applyingat least a portion of said bias voltage negatively to said detector tolimit detection thereby to said modulation components outside said rangeof said light-modulation components, means for utilizing saidcontrol-bias voltage for controlling an operating characteristic oi thereceiver, and means for utilizing said detected components forsynchronizing the operation of said receiver.

12. A television receiver adapted to reproduce a signal-carrier wavehaving light-modulation components and synchronizing-modulationcomponents having amplitude values outside the amplitude range 0! saidlight-modulation components, said carrier wave having a wide range ofsignal-input intensities comprising, a rectifier having a load circuitincluding a voltage divider resistor for deriving from a receivedsignal-carrier wave a control-bias voltage proportional to the intensityof said carrier wave and independent of its light-modulation components.means including a modulated-carrier signal detector for derivingmodulation components from said carrier wave, a connection between saidvoltage divider and said detector for applying a portion of said biasvoltage negatively to said detector to limit detection thereby to saidmodulation components outside said range of said light-mod lationcomponents, means for utilizing all of said control-bias voltage tormaintaining the average signal-output intensity independent of lightmodulation within a relatively narrow range for said wide range ofsignal-input intensities, and means for utilizing said detectedcomponents for synchronizing the operation of said receiver.

13. A television receiver adapted to reproduce a signal-carrier wave theamplitude of which may vary at the receiver and comprising, meansincluding a modulated-carrier signal detector for deriving modulationcomponents from a received signal-carrier wave, means for deriving acontrol efl'ect proportional to the intensity of said carrier wave,means for utilizing a predetermined portion of said control efi'ect forcontrolling said detector to limit detection thereby to a relatedpredetermined portion of the amplitude range of saidmodulationcomponents regardless of variations of the signal-input amplitude tosaid detector, and means for utilizing said detected modulationcomponents. r

MADISON CAWEIN.

